[Zurück]

G. Rogl, K. Yubuta, V.V. Romaka, H. Michor, E. Schafler, A. Grytsiv, E. Bauer, P. Rogl:
"High-ZT half-Heusler thermoelectrics, Ti_0.5Zr_0.5NiSn and Ti_0.5Zr_0.5NiSn_0.98Sb_0.02: Physical properties at low temperatures";
Acta Materialia, 166 (2019), S. 466 - 483.

With a small gap in the density of states and a substantially semiconducting behavior half Heusler alloys have drawn attention as thermoelectric materials. For this study we have selected Hf-free compounds, Ti_0.5Zr_0.5NiSn, Ti_0.5Zr_0.5NiSn (with a densification aid (DA)) and Ti_0.5Zr_0.5NiSn_0.98Sb_0.02 as well their parent alloys TiNiSn and ZrNiSn as cheap thermoelectrics. Electrical resistivity, thermal conductivity and specific heat were evaluated below room temperature (4.2-300 K) in order to get insight into the mechanism of transport properties. SEM and TEM investigations as well as DFT (density functional theory) calculations accompany this research. The fine-grained epitaxial microstructure with a large number of dislocations warrants a low thermal conductivity at ultralow values (~30 mW/cmK at 300 K) at a narrow band gap with a sufficiently high density of states at the Femi level. High order of components mixing strongly affects the stability of the solid solutions by the configuration entropy term, which causes a shrinkage of the miscibility gap. For the electronic density of states (DOS) the split Zr band and impurity Ni band induce a significant reduction of the effective energy gap and thus explain n-type of conductivity of the compounds and solid solutions studied.

Half Heusler alloys, DFT, Nanostructured materials, Specific heat, Thermal effects

http://dx.doi.org/10.1016/j.actamat.2018.12.042